Conventional general-purpose inverters are provided with an inrush current suppression resistor to prevent a large current (inrush current) from flowing to an electrolytic capacitor provided in the main circuit when the power is turned on. During the operation other than when the power is turned on, a relay connected in parallel to the inrush current suppression resistor operates so as to preclude current from flowing to the inrush current suppression resistor to thereby suppress a loss. Further mechanism is arranged such that the relay is disconnected when an alarm is generated, so that the inverter is isolated from three-phase alternating current and damage is suppressed. Here, the relay is placed at a position where current flows most in the inverter and, thus, the temperature of the relay becomes very high. Hence, it is important to suppress the rise of temperature of the relay.
For example, there is a technique in which a certain voltage is applied to the coil of a relay to attract the relay and, then, the voltage applied to the coil is controlled to be lowered to a range within which the attracted state can be retained, so that the rise of temperature is suppressed (for example, Patent Literatures 1 and 2).